Chapter 32, Problem 1ASA

Interpretation Introduction

(a)

Interpretation:

To find the electrode where the oxidation is occurring.

Concept introduction:

Oxidation is the loss of electrons or an increase in the oxidation state of an atom, an ion, or of certain atom in a molecule.

Answer to Problem 1ASA

The oxidation occurs at zinc electrode, because the zinc electrode is negative.

Explanation of Solution

The negative electrode in a voltaic cell is taken to be the one from which electrons are emitted (i.e., where oxidation occurs). The negative electrode is the one that is connected to the minus pole of the voltmeter when the voltage is measured.

Conclusion

Therefore, the oxidation occurs at zinc electrode, because zinc electrode is negative.

Interpretation Introduction

(b)

Interpretation:

To write the equation for the oxidation half-reaction in the cell.

Concept introduction:

Half-reaction is defined as either the oxidation or reduction reaction of a redox reaction. A half-reaction is obtained by considering the change in the oxidation states of individual substances involved in the redox reaction.

Answer to Problem 1ASA

The equation for the oxidation half-reaction is obtained.

Explanation of Solution

Chemical reactions can be classified as oxidation-reduction reactions, because they involve the oxidation of one species and the reduction of another. Such reactions can conveniently be considered as the result of two half-reactions, one of oxidation and the other reduction.

Hence, the equation for the oxidation half-reaction of this cell is written as

$\text{Zn(s)}\to {\text{Zn}}^{\text{2+}}\text{(aq)}\text{+}{\text{2e}}^{\text{-}}\text{(Oxidation}\text{half-reaction)}$

Conclusion

Therefore, the zinc electrode is considered as the oxidation half-reaction of this cell.

Interpretation Introduction

(c)

Interpretation:

To write the equation for the reduction half-reaction in the cell.

Concept introduction:

Half-reaction is defined as either the oxidation or reduction reaction of a redox reaction. A half-reaction is obtained by considering the change in the oxidation states of individual substances involved in the redox reaction.

Answer to Problem 1ASA

The equation for the reduction half-reaction is obtained.

Explanation of Solution

Chemical reactions can be classified as oxidation-reduction reactions, because they involve the oxidation of one species and the reduction of another. Such reactions can conveniently be considered as the result of two half-reactions, one of oxidation and the other reduction.

Hence, the equation for the reduction half-reaction of this cell is written as

${\text{Cu}}^{\text{2+}}\text{(aq)}\text{+}{\text{2e}}^{\text{-}}\to \text{Cu(s)}\text{(Reduction}\text{half-reaction)}$

Conclusion

Therefore, the copper electrode is considered as the reduction half-reaction of this cell.

Interpretation Introduction

(d)

Interpretation:

To write the net ionic equation for the spontaneous oxidation-reduction reaction that occurs in the cell.

Concept introduction:

The net ionic equation is obtained by combining both oxidation and reduction-half reactions in this cell.

Answer to Problem 1ASA

The net ionic for the spontaneous oxidation-reduction reaction is obtained.

Explanation of Solution

When we connect a voltmeter between the two electrodes, we will find that there is a voltage, or potential, between them. The magnitude of the potential is a direct measure of the chemical tendency, or more properly the thermodynamic driving force, for the spontaneous oxidation-reduction reaction to occur.

Hence, the net ionic for the spontaneous oxidation-reduction reaction that occurs in this cell is written as

$\text{Zn(s)}\text{+}{\text{Cu}}^{\text{2+}}\text{(aq)}\to {\text{Zn}}^{\text{2+}}\text{(aq)}\text{+}\text{Cu(s)}\text{(Net}\text{ionic}\text{equation)}$

Conclusion

Therefore, the oxidation and reduction reaction of zinc and copper electrode is considered as the net ionic equation of this cell.